1. Field of the Invention
This invention relates to a process for hydrocracking a petroleum fraction employing a particular type of zeolite to provide a product having a high volumetric heat of combustion.
2. Background of the Art
Jet fuels are employed in a method of combustion wherein fuel is continuously introduced into and continuously burned in a confined space, for the purpose of deriving power directly from the hot products of combustion. Jet engines typically consist of a propulsion or jet tube, plus a gas turbine which extracts sufficient energy from the departing gases to drive the compressor. In present commercial forms, the compressor and turbine are assembled axially upon a common shaft, spaced far enough apart to permit a number of combustion chambers to be arranged about the shaft between the compressor and turbine, with an exhaust tube extending rearwardly from the turbine. The principal application of such engines is in powering aircraft, particularly for high-altitude operations. Therefore, the desiderata of fuels utilizable in jet combustion devices are many and varied.
Jet combustion fuels, as contemplated herein, are hydrocarbon fractions that can have initial boiling points as low as about 200.degree. F. or lower, and end-boiling points as high as about 600.degree. F. Depending upon the particular application, a jet fuel can boil within a relatively low range of temperatures or within a relatively high range of temperatures. For example, in order to insure quick starting in the operation of military jet-propelled aircraft, jet combustion fuels that boil within rather low temperature ranges are used. These fuels, however, have a high A.P.I. Gravity, and accordingly, they will have less weight per gallon. As the weight per gallon together with the number of b.t.u. per unit weight is determinative of the amount of power per gallon of fuel, it is desirable to have the A.P.I. Gravity as low as possible.
In order to improve aircraft performance, the aviation industry in general, and the military in particular, are interested in high density jet fuels which can provide a higher volumetric heat of combustion. A new jet fuel, JP-8X has been proposed, which has a density much higher than that of the current JP-8 fuel.
Use of hydrocracking to increase jet fuel supplies is not new. Zeolites, both natural and synthetic, crystalline aluminosilicates, are typically employed as catalysts for hydrocracking, as well as for other processes. The feature which gives zeolites their special utility as catalysts is that they are porous microcrystalline structures. Pore size and shape determine the selectivity of a particular type of zeolite for particular reaction products. Catalytic behavior of a zeolite is also affected by the composition, i.e., its silica/alumina ratio. Zeolites are often used in conjunction with other materials, such as metals, e.g.,platinum, nickel, molybdenum, tungsten and/or oxides, e.g., Al.sub.2 O.sub.3, SiO.sub.2.
The crystal structure of zeolites may be determined by x-ray diffraction analysis, which gives a diffraction pattern unique to each type of zeolite.
With respect to hydrocracking, catalysts, including various zeolites, have been used in the past.
U.S. Pat. No. 4,875,992 (Hamner) describes a process for making high density jet fuel by contacting a hydrotreated aromatic feedstock with a fluorided Group VIII metal on alumina catalyst.
U.S. Pat. No. 4,764,266 (Chen et al.) discloses a hydroprocessing scheme in which high boiling fractions such as gas oil and cracked cycle oils are converted into jet fuels and naphthas suitable for reforming into high octane gasoline by hydrocracking with a large pore zeolite X or zeolite Y catalyst followed by hydroprocessing with zeolite beta.
U.S. Pat. No. 4,486,296 (Oleck et al.) describes a process for hydrocracking and dewaxing hydrocarbon oils using a catalyst comprising a hydrogenation metal, zeolite beta, and other zeolites.
U.S. Pat. No. 4,612,108 (Angevine et al.) discloses a hydrocracking process for feedstocks containing high boiling waxy components using a number of sequential beds of hydrocracking catalyst based on zeolite beta.
U.S. Pat. No. 4,435,275 (Derr et al.) discloses a hydrocracking process for aromatics production employing a zeolite in conjunction with a metal of Group IVA or VIIIA.
U.S. Pat. No. 3,923,641 (Morrison) discloses a process for hydrocracking a naphtha fraction using a zeolite beta.
U.S. Pat. No. 3,150,071 (F. G. Ciapetta et al.) discloses a jet combustion fuel produced by hydrocracking a hydrocarbon distillate fraction using a platinum or palladium type catalyst on a refractory oxide support.